C-flat: At home, the earliest music we play is from the 1100's - the song "Singer's Sing" which has a melody like Gregorian chant. also the Cantigas de Santa Maria from Spain.At the Texas Toot music tends not to be so old because the classes like stuff with parts. Most is from the 1500 - 1600's, though there was a class in Spanish music which went further back.
As for where it comes from - the Internet, public library; books of music from music stores, especially books for recorder; friends; recordings and church hymnals.
My Noteworthy software really gets a workout getting this music ready for the group.